1. Field of the Invention
The present invention relates to a drive device, and more particularly to a drive device using a piezoelectric element.
2. Description of the Related Art
A digital camera or the like moves the lenses of a lens unit in the optical axis direction thereof for the zooming, the focusing, and the like of the lens unit. An electromagnetic motor is used as a power source of the movement (see, for example, Patent Literature 1: Japanese Patent Application Laid-Open Publication No. 2005-91782). Because the electromagnetic motor generates noise at the time of a drive thereof, however, there is the problem of resulting in recording the noise of the electromagnetic motor at the time of moving the lenses with the electromagnetic motor at the time of photographing a moving image. On the other hand, an ultrasonic motor, generating less noise is used for moving lenses. Because the ultrasonic motor utilizes the resonance phenomenon of a piezoelectric element, however, the size, the form, the dimensions, and the like of the piezoelectric element are required to be highly accurate at the time of manufacturing the ultrasonic motor. Consequently, it is hard to mass-produce ultrasonic motors inexpensively.
Furthermore, there is a motor described in Patent Literature 2 (Japanese Patent Application Laid-Open Publication No. 2005-130637) as a motor using a piezoelectric element. To put it concretely, piezoelectric elements (1a, 1b) are superposed on a rotation body (3), and the bending and the restoring of the piezoelectric elements (1a, 1b) are repeated. The bending of the piezoelectric elements (1a, 1b) at a low speed, here, causes no slips between the piezoelectric elements (1a, 1b) and the rotation body (3), and the rotation body (3) rotates. After that, the piezoelectric elements (1a, 1b) are restored at a high speed, and a slip is thereby caused between the piezoelectric elements (1a, 1b) and the rotation body (3), and the rotation body (3) does not rotate.
The technique described in Patent Literature 2, however, realizes the bending of the piezoelectric elements (1a, 1b) by providing the piezoelectric elements (1a, 1b) in the rotation axis direction of the rotation body (3) over a long distance. Consequently, the thickness of the whole device is led to increase in the rotation axis direction.
Furthermore, because the bending of the piezoelectric elements (1a, 1b) makes the lengths of the piezoelectric elements (1a, 1b) along the rotation axis direction of the rotation body (3) change, the rotation body (3) is led to vibrate in the rotation axis direction.
Accordingly, it is an object of the present invention to enable the length of a drive device along the rotation axis direction of the rotor of the rotation body (3) and the like to be made to small, and to make vibrations of the rotor like that not generate.